The present invention relates to a stencil printer or similar printer and more particularly to a color printer including a plurality of print drums around which masters are to be wrapped.
A thermal, digital master making type of stencil printer belongs to a family of relatively simple printers. In this type of stencil printer, a stencil is caused to contact a thermal head having fine heat generating elements arranged thereon. While the stencil is conveyed, the heat generating elements are selectively energized in accordance with image data so as to selectively perforate the stencil with heat. The perforated stencil, or master as referred to hereinafter, is wrapped around a print drum implemented as a porous hollow cylinder. Ink feeding means arranged in the print drum feeds ink to the inner periphery of the print drum. A press roller or similar pressing member presses a paper sheet or similar recording medium conveyed thereto against the print drum via the master. As a result, the ink is transferred from the print drum to the paper sheet via the porous portion of the print drum and the perforation pattern of the master, printing an image on the paper sheet.
Assume that a master making device and a master discharging device are physically separate from the printer, that the print drums of the printer are mechanically interlocked to each other, and that all of the print drums are removed from the printer in the event of master making and master discharging and again inserted into the printer. Then, the print drums cannot be removed from or inserted into the printer at the same time unless the distance between nearby print drums is an integral multiple of the circumferential length of each print drum in order to provide all of the print drums with an identical home position. This, however, makes the entire printer bulky. In light of this, the distance between nearby print drums may be made shorter than the circumferential length of each print drum with a preselected initial phase difference provided between the drums, thereby making the printer compact. This kind of scheme is taught in, e.g., Japanese Patent Application Nos. 9-321702 and 10-167322 and Japanese Patent Laid-Open Publication Nos. 11-138961 and 11-151852.
Specifically, the above Laid-Open Publication Nos. 11-138961 and 11-151852 disclose technologies that free the operator of a single drum type stencil printer from troublesome operation in the event of color printing. Further, assume that a color stencil printer including a plurality of print drums produces, e.g., a tetracolor or full-color print. Then, the operator of such a printer sometimes desires to replace two print drums assigned to a first and a second color, respectively, at the same time or to remove a paper sheet jamming a path between the two print drums without scratching mesh screens wrapped around the drums. To meet such a demand, in a printer of the previously described type spacing nearby drums by a distance shorter than the circumferential length of each print drum and providing an initial phase difference between the print drums, the above technologies automatically move the individual print drum to a dismount position by using top-bottom movement adjusting means including top-bottom moving means. The top-bottom movement adjusting means is essential for multicolor printing.
However, the problem with Laid-Open Publication No. 11-138961 is that the top-bottom movement adjusting means must rotate the individual print drum by a phase corresponding to the circumferential length of several ten millimeters or to adjust the top-bottom movement (amount of phase adjustment) by an angle of 90xc2x0 or more with the top-bottom moving means. The adjusting means therefore makes the printer bulky although the initial phase difference makes it compact.
Moreover, the above conventional technologies have been proposed in the initial stage of development and, of course, have various problems left unsolved as to making the operation easy and efficient for the operator to perform.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Utility Model Laid-Open Publication No. 64-46258, Japanese Patent Laid-Open Publication Nos. 5-229243, 6-71998, 6-293175, 7-1817 and 7-17013, Japanese Utility Model Laid-Open Publication No. 61-85462, and Japanese Patent Laid-Open Publication Nos. 8-39916, 8-39918, 10-109470, 10-846, and 64-18682.
It is therefore an object of the present invention to provide an improved compact printer not needing the top-bottom movement adjusting means and allowing a plurality of print drums to be mounted thereto by simple operation.
It is another object of the present invention to provide a printer that is easy and efficient to operate.
A printer of the present invention includes a plurality of drum units removably mounted to a printer body and each including a respective print drum allowing a particular master to be wrapped therearound. Nearby print drums are provided with a preselected initial phase difference therebetween beforehand when the drum units are present in the printer body. The drum units each are removable from the printer body when the respective print drum is brought to a preselected phase. The printer wraps masters around the print drums, feeds ink of particular color to each master, and presses a recording medium against the consecutive masters to thereby effect continuous printing. Individual removal setting devices each are assigned to a particular drum unit for making the drum unit removable from the printer body. Angular position sensing means each sense the angular position of the drum of a particular drum unit. A drum drive arrangement causes the print drum of the drum unit to be removed to rotate. A controller controls, based on the output of the individual removal setting device assigned to the drum unit to be removed and the output of the angular position sensing means assigned to the print drum of the same drum unit, the drum drive arrangement such that the print drum of the drum unit to be removed is brought to the preselected phase.